As industries are developing, and competitions become violent, demands for convenient and reliable steganography increase. In particular, a sympathetic printing method using a sympathetic ink promotes new demands for anti-forgery techniques in the field of securities or exchange checks. Sympathetic printed-matters using a sympathetic ink are advantageous in that a confidentiality status can be easily checked because whether or not a printed matter has been read by any other person can be easily confirmed. The term “sympathetic” means a phenomenon in which something is invisible on application or soon but can be visible later by developing the hidden parts. The sympathetic printed-matter is a printed matter produced using a sympathetic ink, on which a script written with a sympathetic ink can be visualized through heating or other methods such as a chemical reaction. The sympathetic ink may include a body fluid such as blood, saliva, sweat, and urine, various foods or compounds containing acidic or basic properties such as vinegar, fruit juice, sodium bicarbonate, salt, sugar, rice, aspirin, Arabian gum, boric acid, starch, ammonia, magnesium sulfate (epsom salts), caustic silver, soap, glue, or adhesive. As a representative material of the sympathetic ink, lead acetate (Pb(CH3COO)2) is known in the art. The lead acetate has a colorless crystalline material obtained by dissolving lead monoxide (PbO) or tri-lead tetra-oxide (Pb3O4) in acetic acid. A sympathetic ink is obtained by dissolving the lead acetate in an alum solution. As a method of visualizing hidden contents written on a sympathetic printed-matter, there are known an optical method in which a hidden part is visualized by irradiating light using a special light source such as infrared or ultraviolet rays or irradiating such light at a particular angle, a mechanical method in which a hidden part is visualized by dispersing minute powder such as graphite and sweeping away the powder, and a physical chemical method in which a hidden part is visualized by exposing the sympathetic printed-matter in the hot air, fumes, or vapors of a chemical agent or immersing it in a chemical agent. The sympathetic printed-matter using a sympathetic ink of the related art is based on an irreversible sympathetic phenomenon in which the printed part appears and does not disappear continuously thereafter. Even when it is reversible, it is difficult to know whether or not the hidden part of the sympathetic printed-matter has been already read by any other person. In addition, it is necessary to provide a separate reagent or tool for visualizing the hidden part on the sympathetic printed-matter.